1. Field of the Invention
This invention relates to conductive polymer compositions and electrical devices containing them.
2. Summary of the Prior Art
Conductive polymer compositions comprising carbon black dispersed in a polymer are known. Depending on the polymer and the carbon black and the relative amounts thereof, the compositions may have room temperature resistivities ranging from less than 1 ohm.cm to 10.sup.8 ohm.cm or more, and may exhibit positive temperature coefficient (PTC) behavior, zero temperature coefficient (ZTC or constant wattage) behavior or negative temperature coefficient (NTC) behavior. The major uses for conductive polymer compositions are in the shielding of cables and the inhibition of electrostatic charges, but the compositions can also be used in electrical devices in which current passes through an element composed of the composition, e.g. in heaters and current-limiting devices. Compositions useful in electrical devices generally have different properties from compositions useful in shielding and electrostatic applications. Reference may be made, for example, to U.S. Pat. Nos. 3,823,217 (Kampe), 3,861,029 (Smith-Johannsen et al.), 3,950,604 (Penneck), and 4,177,376 (Horsma et al.) and to U.S. patent application Ser. Nos. 904,736 (Penneck et al.), 732,792 (Van Konynenburg et al.), now abandoned, 751,095 (Toy et al.), now abandoned 798,154 (Horsma), now abandoned, 965,343 (Van Konynenburg et al.), now U.S. Pat. Nos. 4,237,441, 965,344 (Middleman et al.), now U.S. Pat. Nos. 4,238,812 965,345 (Middleman et al.), now U.S. Pat. Nos. 4,242,573 6,773 (Simon) now U.S. Pat. Nos. 4,255,698, and 75,413 (Van Konynenburg) now U.S. Pat. No. 4,304,987. The disclosures of these patents and applications are incorporated by reference herein.